就是用平方差公式.
(x+y)^2-16(x-y)^2
=(x+y)^2-[4(x-y)]^2
=[(x+y)+4(x-y)][(x+y)-4(x-y)]
=(x+4x+y-4y)(x-4x+y+4y)
=(5x-3y)(5y-3x)
分解因式 要有详细过程 (x+y)的平方—16（x-y)的平方
就是用平方差公式.
(x+y)^2-16(x-y)^2
=(x+y)^2-[4(x-y)]^2
=[(x+y)+4(x-y)][(x+y)-4(x-y)]
=(x+4x+y-4y)(x-4x+y+4y)
=(5x-3y)(5y-3x)